Heat treatment for selective laser melting of Inconel 718 alloy with simultaneously enhanced tensile strength and fatigue properties

Abstract

Inconel 718 alloy fabricated by selective laser melting (SLM) was used to investigate the evolution of precipitated phase from as-SLM to heat-treated (HT) samples. A heat treatment, including homogenization, solution and aging heat treatments, was proposed to obtain SLMed Inconel 718 alloy components for desirable mechanical performance. Post heat treatment process can reduce the number of original print defects due to grain boundary migration and grain growth. The solid solution plus double aging treatment (HT-1) results in the precipitation of large amounts of δ phase within the grain and at grain boundaries, as well as a small amount of massive MC. Homogenization, solid solution plus double aging (HT-2) eliminated a large amount of internal δ phases in the grain as well as needle-like δ phases at grain boundaries. However, the single aging (HT-3) still retains some of the needle-like δ phase. Heat-treated specimens increased tensile strength by 20–24% at room temperature and maintained high strength at 650 °C compared to the as-SLM. Further fatigue results also confirmed that the HT-2 treatment increases the fatigue life by an order of magnitude compared to the as-SLM to 10 8 cycles at a stress amplitude of 300 MPa. This work is anticipated to provide a potential route to obtaining attractive mechanical properties for SLM superalloy components. • The evolution of precipitated phase in SLMed Inconel 718 alloy under different heat treatment systems was studied. • Post heat treatment significantly improves strength of SLMed Inconel 718 alloy and maintains the high strength at 650 °C. • HT-2 heat treatment significantly increases the ultra-high cycle symmetric bending fatigue strength and life of the specimens .